I have a feeling you might be talking about two different things?
- Type 1.5 is slow onset type 1 - the insulin producing beta cells are dying off, but slowly, so type 1.5s have a long honeymoon period where they are making their own insulin for a while. Sometimes a type 1.5 might have a particularly strong honeymoon and be able to avoid insulin for a little while, but they will become insulin dependent eventually.
- "Double diabetes" is where someone is type 1 AND is insulin resistant - not sure where you have read that that is not possible, but unfortunately it is possible for a type 1 to be insulin resistant, for the same reasons anyone else might be insulin resistant - weight, activity, hormones, shift work, stress etc etc
Sounds like your consultant is saying you might have double diabetes - which is a different, separate, thing from type 1.5