The short answer is "yes". And, generally, the code will be a bit slower.

But sometimes a proper OO-ish refactoring will reveal optimizations that make the code faster. I worked on one project where we made a complex Java algorithm much more OO-ish, with proper data structures, getters, etc. instead of messy nested arrays of objects. But, by better isolating and restricting access to the data structures, we were able to change from giant arrays of Doubles (with nulls for empty results) to more organized arrays of doubles, with NaNs for empty results. This yielded a 10x gain in speed.

The short answer is "yes". And, generally, the code will be a bit slower.

But sometimes a proper OO-ish refactoring will reveal optimizations that make the code faster. I worked on one project where we made a complex Java algorithm much more OO-ish, with proper data structures, getters, etc. instead of messy nested arrays of objects. But, by better isolating and restricting access to the data structures, we were able to change from giant arrays of Doubles (with nulls for empty results) to more organized arrays of doubles, with NaNs for empty results. This yielded a 10x gain in speed.

Addendum: In general, smaller, better structured code should be more amenable to multi-threading, your best way to get major speedups.