It's legal and doable, but tight - some gates in T3 are miles away so long walking could be involved.

I would say it;s fine as long as you are happy to accept the risk of misconnect. BA1516 is a 10.15 flight to JFK. Since there are loads of further flights to JFK after that, it shouldn't be a problem if you miss it.

Of course the flipside of the above is that since there are lots of later flights to JFK, it may be more sensible to choose one of those now and reduce the risk of hassle on the day. Up to you I guess...

Clearly if you absolutely have to be in NYC by a certain time, or you're travelling on a busy day like the Friday before Christmas when later flights may be full, then a longer connection is imperative.