1500 wet is not very aggressive at all, but if you're worried about it, go with 2000. The idea is to give it a surface to bond too. Give it a good 24 hours before sanding.
That said, you may be over complicating things....If you're happy with how the base coat is laid down, I'd be tempted to just spray the clear as is. If you do, it's going to have a tendency to run because the surface is so slick, so start with a couple super light coats (basically just 'fog' it), waiting 5-10 minutes between each.