Depends how much effort I'm putting in and how slowly I'm speaking.
High effort: ins-yu-lin
Normal: ins-uh-lin
In a rush: ins-lin
The poster above who mentioned yod coalescence is correct about the sh sound. (It's also sometimes called palatalisation, but I don't think that's technically accurate.)
Sounds like tyuh, dyuh, syuh etc. are effortful for most English speakers. This means that over time, either the yuh part of the sound (the yod) gets dropped — as in the common pronunciation of "suit" as "s-ooh-t" rather than "syoot" — or the consonant and the yuh sounds get coalesced/changed into a different, easier sound. Tyuh becomes chuh, dyuh becomes juh, syuh becomes shuh, etc. For example, "assure" — many people will pronounce this similarly to "ashore", and you might sound over-fussy if you said "ass-yure". Pretty much everyone does yod coalescence with the dyuh sound in "soldier", but with something like "endure", it's more mixed.
It's a natural process of language change and it's not necessarily better to shift ins-yoo-lin to ins-uh-lin than in-shu-lin.