If you've got external memory then you ain't going to get rid of the ALE signal , since you have to latch the address off the AD bus.

You must have a very poor layout on your board. I have a design with c515 and its latch, RAM and ROM on one side of board with a huge ground plane under the entire system that seems to run pretty quiet

Have you decoupled the supply rails AT the latch with a 0.1 uf ceramic ? Pretty well all of it needs good attention to the power connections. Make sure that you have to radiating loops of supply rail for example.

Steve