In the context of organic chemistry, which type of reaction typically takes longer to reach completion?

Compare with SN1 reactions: SN1 reactions are unimolecular nucleophilic substitution reactions that also involve a carbocation intermediate. Like E1 reactions, the formation of the carbocation can slow down the reaction.

Evaluate E2 and SN2 reactions: E2 reactions are bimolecular elimination reactions that occur in a single concerted step, typically faster due to the absence of intermediates. SN2 reactions are bimolecular nucleophilic substitution reactions that also occur in a single step, generally faster than SN1 and E1 due to the direct attack of the nucleophile.