Starpoints to Aeromexico was a 1:1 transfer,
based on this older article in Forbes... plus the 5000point bonus if you transferred 20k Starpoints.
With the new program, it'll be 3:1, and a bonus of 5000 airline points/miles every 60k Marriott points you transfer... so no change to the amount of Starpoints required compared to the old program since 1 Starpoint = 3 points..
Are you sure your original calculations were correct?
14,500 Aeromexico points = 14,500 Starpoints = $14,500 spend on the old SPG card, since it was $1 per Starpoint unless that spend was at a hotel.
As pointed out by @
stromile below, you weren't able to transfer SPG Starpoints to Amex Membership Rewards Points before.. .it was a one way transfer from AMEX to SPG at 3:1.
In the new program, to get 14,500 Aeromexico points, you'd need 43,500 Marriott points, which means $21,750 spend, if your spend doesn't include bonus points.
14,500 Aeromexico points = 43,500 Marriott Points = $21,750 spend on new SPG card at 2pts/$1.