Would you say that one and a half times the bolt diameter would suffice for embedment in concrete with epoxy bonding?
Of couse not. Obviously, bolt length is a factor in such a design.
All the stress that the bolt is holding has to go thru the first "length" of 1.5 * dia. this is comparable to the weakest link in a chain. If the first length can not do the job, you have the wrong bolt. It really does not matter if the bolt was one mile long.