Agreed with everyone else. Sacrificing your car just b/c you're engaged is a bad idea....Especially since it's not necessarily your idea. If you had a kid on the way, that makes sense, but not just b/c you're getting married.
Keep the car and find somewhere else to save money. Besides like it's been already stated, you won't be saving much if anything by swapping out cars. You don't want to resent your fiancee if you end up hating the LGT and you're not saving any real money.
I am recently engaged and the one thing that my finacee doesn't bother me about are the cars. Although I did promise not to buy another car for 5+ years when I got my 2011.....but you never know