The Suggestion

This seems inefficient and will perform increasingly worse the larger the pack is as more and more structures are added to the registry.

Why Should It Be in the Mod?

The solution would be to either cache the structures that you're interested in from the registry or use a structure tag to collect your structure together and then grab the entries of the tag when needed instead of looping the whole registry. Example:
https://github.com/TelepathicGrunt/RepurposedStructures/blob/8b65df28e4ef45a0a2918b0cf93485921218299b/common/src/main/java/com/telepathicgrunt/repurposedstructures/mixins/features/NoVinesInStructuresMixin.java#L41

Please Read and Confirm the Following

• I have confirmed this suggestion is unique and has not been suggested already.

There's a cache

Hmm I miss read the code. Does the cache bust on world exit and re-entering?

It's a WeakHashMap