Sorry to hear your awesome vet is out of reach.
Are you feeding him the adult dry/wet or the senior dry/wet?  If he is over
6 I'd recommend to use the senior since cats of that age become less active
and don't need as much energy
Are there any other concerns with your cat?  Does he drink/urinate a lot
(one sign of diabetes)? Difficulty breathing (too much fat impinges on the
ability of the lungs to expand)? As I don't live in Fl I don't know any good
vets down there, sorry.
All I can say is keep looking.  I don't know if Gainesville is anywhere near
you, but there is a vet college there and the vet schools are always full of
vets and student vets that are concerned and love your pet.
If you are using wet food, I'd recommend giving at least 1/2 the daily need
in dry and 1/2 wet (better for their teeth - and less smelly in the litter
box).  I use only dry myself unless I need to give medication crushed up in
something.
If you are using adult lite, switch to senior lite at the recommended
amount.  Try it for 4 weeks.  If there is not a drop in weight (like 1/2 -
1lb) then decrease the amount a little every 2 weeks until you find the
amount that your cat loses weight on.
Please don't let him lose too much too fast.  Even if your cat was 15 lbs if
he loses 1 lb per month that's like a 150lb person losing 10 lbs in a month
(2.5 lbs/week) which is a lot.
I'd still like to see your cat getting checked out by a vet because if there
is something medically wrong with him, all we'd be doing by putting him on a
diet is possibly hiding an illness or even exacerbating it.
Good luck!

Hi from Orlando....
We have found a fabulous vet
DR GREG MURRAY
Aloma Jancy Animal Hospital
407-671-1183

DRLUV