Silicone Coulping to PVC Male Adapter?

I have a tub drain installed to 1.5" PVC Male Adapter via a 1.5" silicone flexible coupling.
It is tightened down well enough to where it is not leaking. I filled the tub to capacity and allowed it to drain and still there are no leaks. Will this setup hold-up well over time?

I included a makeshift diagram of what i did...

Not an approved connection for two reasons:
► although you seem to have no leaks, the manufacturer defintely specifies that coupling for use on a smooth pipe, not on threads.
► a coupling like that should not be in an inaccessible location. The drawback with it is that if you ever have to cable the drain, the head of the snake may poke through the rubber. You need to get rid of the male adapter, and use stainless steel banded flex, with two different ends, one for tubular, one for IPS.

A plumber would be able to install this without flexible couplings, but at a minimum, you should do it as I described.

Why on earth would you use a threaded adapter? And beyond that, why use a "silicone" (not silicone) coupling anyways?

I am installing an American Standard tub with an overflow that's mounted at an angle from the existing plumbing, so I used the flexible coupling for some flex. But, I think I'm going to re-do this...thank for the quick reply guys...

The overflow MAY be on an angle, (but I have never seen one like that), but the pipe coming down from the drain tee is NOT at an angle. That "Fernco" coupling is not meant to fit over threads, and is not intended for use ANYWHERE inside a building.