It seems pretty clear that they do only minimal live testing during the "open a ticket, implement something, deploy it in production, all while the customer is still on the call" cycles. So your second concern is probably not relevant in this particular setting.

Regarding the first, I think you're probably right, but then again, if there is a 15-minute base cost, it's hard to amortize that through fewer incremental runs of the compiler.

(Which isn't to say that I think they are doing the right thing.)