Ive done all the math, included is a list of each pokemon's base speed stat.

Speed stat (In order of Evo, form changes have dashes):

Rowlet Line: 42, 52, 70,
Litten Line: 70, 90, 60,
Poplio Line: 40, 50, 60
Pikipek Line: 65, 75, 60
Yungoos Line: 45, 45
Grubbin Line: 46, 36, 43
Crabrawler Line: 63, 43
Oricorio: 93
Cutiefly Line: 84, 124
Rockruff Line: 60, 112/82
Wishiwashi: 40/30
Mareanie Line: 45, 35
Mudbrey Line: 45, 35
Dewpider Line: 27, 42
Fomantis Line: 35, 45
Morelull Line: 15, 30
Salandit Line: 77, 117
Stufful Line: 50, 60
Bousweet Line: 32, 62, 72
Comfey: 100
Oranguru: 60
Passimian: 80
Wimpod Line: 80, 40
Sandygast Line: 15, 35
Pyukumuku: 5
Type: Null Line: 59, 95
Minior: 60/120
Komala: 65
Turtonator: 36
Togedemaru: 96
Mimikyu: 96
Bruxish: 92
Drampa: 36
Dhelmise: 40
Jangmo-o Line: 45, 65, 85
Tapu Koko: 130
Tapu Lele: 95
Tapu Bulu: 75
Tapu Fini: 85
Cosmog Line: 37, 37, 97/97
Nihilego: 103
Buzzwole: 79
Pheromosa: 151
Xurkitree: 83
Celesteela: 61
Kartana: 109
Guzzlord: 43
Necrozma: 79
Magearna: 65
Marshadow: 125

Add all numbers up to get 5690, divide by the number of pokemon (including ulternate forms with various stat changes)
Average speed: 67.7