You should. As an oil based glaze should only be used directly on bare paint. An acrylic glaze can be used after a sealant, but will just wash off. If you were at a show and wanted your paint to look wetter, you can leave it glazed. But after that, you should either seal/wax over an acrylic glaze. Leaving a glaze as you LSP is pointless IMO. Unless you just want to take tarty photos of how glossy your paint looks.
Firstly GTechniq C1.5 is not an Oil based glaze. C1.5 can also be used to seal your paint. Same as you can with C1 & C2.
C1 will give around a years worth of protection
C2 will give around 8 months of protection
C1.5 will give around 6 months of protection
The reason i used C2 first as that gave the most amount of protection. Then layering 2 layers of C1.5 over the top just adds gloss to it. If you look at the labels on C1.5 and C2 they say they can be layered over the top of other waxes/sealants. So although i have called it a glaze it isn't a glaze per se
My understanding of the process is you always seal the paint first as this locks in the polishing you have done by Machine/Hand. You then add a wax for durability and a glaze for Gloss.
Another example is Wet Glaze 2.0
This specifically states that you can Seal, Wax, Glaze, Wax, Glaze as it doesn't contain any cleaners it is purely a gloss enhancer.