Slightly complicated situation, but would really appreciate any advice.
I have an Indian passport, with Indefinite Leave to Remain in an old passport.
Recently I've got married, and taken on my husband's surname, but kept my maiden name as a middle name - eg. was Jane Doe, now Jane Doe Smith - I've got a new Indian passport in that new name, including listing my spouse in my passport (who is a British citizen)

I've applied for a BRP card in early December 2018 via the standard (non priority) service, and have been told that this may take upto 6 months to process. This hasn't come through yet and I have no idea what reasonable timescales are as when I call they just say it could take upto 6 months.

My question is - in the meantime, I would like to plan a holiday to Europe - am I able to get a schengen visa in my new passport, using my old IDLR stamp + new passport + marriage certificate, or do I NEED to wait for my BRP card to come through? The reason I ask is because I know my name has changed (therefore need new BRP), but I still have my old surname in my new name, just as a middle name now instead - so could my IDLR stamp still be valid?

Thanks for your replies!