For well designed relational databases, foreign key (FK) constraints are not optional. They play a significant role in maintaining referential integrity. Having stated that principle, it is possible to place too many FK constraints on a given table and significantly degrade performance. However, this is most often a symptom of poor database design and not an indictment of FK constraints.
If you are concerned that specific FK constraints may degrade performance, then generate and examine the query execution plans for all related CRUD statements.
If the evidence points to FK constraints as being the root cause of the bottleneck, then refactor the physical database schema with the aim to reduce the number of FK constraint on a given table, but without sacrificing overall referencial integrity (enforced by the FKs).