Modify follow limit 7500 -> 15000

app/validators/follow_limit_validator.rb

 # frozen_string_literal: true
 
 class FollowLimitValidator < ActiveModel::Validator
-  LIMIT = ENV.fetch('MAX_FOLLOWS_THRESHOLD', 7_500).to_i
+  LIMIT = ENV.fetch('MAX_FOLLOWS_THRESHOLD', 15_000).to_i
   RATIO = ENV.fetch('MAX_FOLLOWS_RATIO', 1.1).to_f
 
   def validate(follow)