If I compare Maple24 and Maple22 on the exact same worksheet, Maple22 executes twice as fast as Maple24.
For my kind of work this is very serious. I have programs that can take 10 or more days to complete calcuations, therefore what Maple22 will calculate in 10 days, Maple24 takes 20 days. It has wasted a LOT of my time, whatever the reason is.

Here is the code: 
1) MM must be a high order series expansion with complex arguments so that simplification is not trivial. Use any such asymptotic expansion.
NOTE: I can supply an expansion for a developer through official Maple support, but cannot release it publicly as it is part of a future publication. It is easy enough for anyone to create a complex expansion, with difficult simplification.
2) The simplification of the expansion must at least take a couple of minutes at e.g. Order=10 for the comparison to make sense.
3) Then run the program for Maple22 and Maple24 respectively and note execution time.
4) This was run on Linux.

As you will see the Maple24 calculation takes twice as long as the Maple22 calculation. 
SEE RESULTS AT END OF PROGRAM.

 

testorder:=6;                             # Enter the expansion order here.
MM:=??:                                   # Enter the expansion here.
series(MM, x = 0, testorder):
convert(%, polynom):
map(simplify, %):
#collect(%, x, simplify):
simplify(%):

                        testorder := 6

RESULTS:

OPTION1 Calculation time for series MM,

Maple24
O(4):   Linux Wall-Clock Time: 1.000 seconds
O(6):   Linux Wall-Clock Time: 11.000 seconds
O(8):   Linux Wall-Clock Time: 153.000 seconds
O(10): Linux Wall-Clock Time: 2135.000 seconds 
O(12): Linux Wall-Clock Time:  19593.000 seconds

Maple22
O(4):   Linux Wall-Clock Time: 0.000 seconds
O(6):   Linux Wall-Clock Time: 9.000 seconds
O(8):   Linux Wall-Clock Time: 88.000 seconds
O(10): Linux Wall-Clock Time: 1062.000 seconds 
O(12): Linux Wall-Clock Time: 8987.000 seconds