I'm sure you'd be ok with 15mm all round.
Monzas are 7.5 et51
I've got BBS VZ - 8 et44 - which are a lovely fit. No rubbing.
Doing the sums, your Monzas are about 13mm more tucked than my VZ.
Therefore, 15s all round on your Monzas would make them poke 2mm more than my VZ.
Would I get away with a theoretical 2mm spacer all round? Yes. Easily.
Oh and I'm down 30mm on H&R 29176 springs.