My worry is that if I switch the chipmunk, I will lose the experience I have in the 152 as I will have to relearn the manouvers in a much more agile aircraft
Best lost IMHO.
Last time i flew the Chipmunk, the controls didn't come naturally, as I have most of my hours in 152's, so I'm worried it'll take me a long time to feel comfortable in the aircraft.
Seriously? You probably found them a little sensitive compared with the Chippy, but you will get used to the latter very quickly. It's the best harmonised light aircraft ever made. You're comparing a Vauxhall Corsa to a Morgan.
Pay for the Chippy and become a better pilot!