Before Irma it was pretty slow with too many people using it. This might have changed since then (now there are less slips and no
fuel dock); but there are alternatives as Nicholson58 has written - plus some of the bars/restaurants in the area will have WiFi that you might get at your slip for the
price of a
beer or drink to get their password.
I'm at a different IGY Marina right now and the WiFi is superb - I can do videoconferencing until about 09:00 when the others start using the web and it remains fast enough for just about everything else all the time. My backup is a paid-for data account with digicel and a mifi device. That is also available on St. Martin although perhaps Orange might have better coverage there.