What kind of shrimp? 1.5 seems a bit small to breed anything but opae ula. The 5 gallon if set up properly will be okay for most of the hardier species (and that is a relative term) like a lot of the neos.
its possible but the smaller the tank the fast the water will go from good to bad.
I use 4G cubes for when i want to selectively breed specific shrimp and then put them back into general population after I see the female is berried.
i breed crs pretty well in a 1.5 gal cube. im one of the lucky ones that tends to do well with small nano tanks and shrimp. it is a bit harder to keep stable parameters in smaller tanks that is why most go with bigger volume of water.