I actually think that you raised too fast from 1.5 to 1.75u. Right now, the 300s look like rebound, not lack of duration. The important thing will be to not decrease back to 1.5u on a 300, but when you get one of those PSs in the 100s. Nadirs can vary wildly with lev (and, I thnk, lantus). Although a nadir at about +8 is maybe most common, I have seen everything from early to late. Earlier ones may actually be very late nadirs off the previous dose. Definitely an ECID thing. (I know you didn't ask for dosing advice...)
As for switching and convincing the vet, there might be articles linked in the Lev 101 sticky that you could print out and give to him/her.
People switching to lev from lantus have found that their kitty doesn't swing as much, that they are calmer/happier (if grumpiness was an issue on lantus). Lev is ph neutral so doesn't sting at the shot sight and may be gentler overall, although that is subtle in most cats, it can be dramatic in others.