Talk to their choirmaster.
This isn't an official Ordinariate usage, but likely is how these people think (mistakenly, of course) that this chant should be sung. They may think that it's very meditative or prayerful. They may think a variety of things.
A friendly but serious talk with the choirmaster may yield improvement - unless he or she really is convinced of what they are doing.

What parish is this, and where?

Two things come to mind:

1) I assume that the Choirmaster must know something about music -- the chances that a parish of the Anglican patrimony (Catholic or otherwise) would get someone who knows nothing is rather slim -- however, assuming he knows something about chanting in particular, he might be used to chanting, or hearing chant, in a large reverberant space, where a slower tempo might be needed; however, the average parish church does not have the acoustics of Westminster or Ely, and so a faster tempo is needed (this applies equally to chanting and to well modulated speaking).

2) He could also know nothing about chant, but an awful lot about figured music, and might well be conducting the chant in a kind of perpetual 1-1-1-1-1-etc. pattern, where every note is a down-beat, and every beat is the same. This will slow down the chanting to a ponderous speed, and in a dry acoustic is deadly.

Also, there are some people who for some reason think that music (plainchant or figured music) is only "prayerful" if sung ssslllloowwwllllyyyyyyy (and softly). This is hogwash. It's tedious, and I think, in all honesty, that these people assume the eyeballs of congregants rolling into the backs of their heads from boredom to be a sign of ecstasy.

I have a theory that a lot of otherwise very competent Anglican organists are suffering from a disconnect between the room they imagine and the room they are in at any given moment.

My other theory is that a lot of them used to be Presbyterian and hate happiness.

Adam Wood FTW.

Don't forget the defensiveness that comes with it if it is even gently probed - with past different practice of prior organists being quite sniffed at.

Tangent: https://en.wikipedia.org/wiki/Robot_Patent

I'll take this opportunity to respectfully mention that how chant "should" be sung is subject to a number of factors, acoustic as mentioned above being only one of them. Gregorian chant is very old (perhaps the understatement of the century), and depending on the century or region it was indeed sung in a very different way than the way most 21st-century persons would say it "should" be sung. I daresay that the Solemnes method is not the only way to sing chant, or perhaps even the most appropriate way today, or even the most historically accurate way (again, depending on where you are in history). (I'm not trying to bash the Solemnes method specifically, especially since it has not yet been mentioned in this thread; nevertheless, since the Solemnes sound forms the basis for "the way to sing chant" in much of contemporary liturgical musical thought, I thought it worth noting that it's not the only way to do it.) None of this is to say that the choir in questions isn't singing too slowly for the acoustic/congregation/particular melody in question—it's rather to place the discussion in a greater context, one that perhaps calls into question what the "ideal" chant "should" sound like—if indeed there is an "ideal" chant sound at all.

Having spent a year and a half in a Benedictine run institution where chanting is a regular part of daily life for monks, students, and faculty, I find most chant to be rather disappointing in comparison. To chant with those you live every day, studying, singing, praying, and relaxing with is one experience. To chant with those you spend at most an hour a week practicing with and otherwise barely know is entirely another, at best a pale shadow of the deeper reality. Yet, even that pale shadow calls to mind those happier times, and so while it is a disappointment in one sense, it is a welcome reminder, and a hint of a foretaste of things that may be to come.

Noel is correct. Sometimes, they don't have ANYONE given how small some of the Ordinariate groups are. The chanting of things like the responses at the preface then are taken up by the congregation during Mass which can drag. God bless them for trying their best! If only similar attempts were made in other places.