15. A football team participates in the World Cup, and in a certain match, 11 players start the game, using a 4-4-2 formation (4 defenders, 4 midfielders, 2 forwards). There are 7 substitute players (2 defenders, 2 midfielders, 2 forwards, and 1 goalkeeper). The rules allow for a maximum of three substitutions. If the team maintains the 4-4-2 formation after substitutions, and substituted players do not return to the field, and no players are sent off during the entire match, it is found that the two main forwards and the goalkeeper play the entire match, and substitutions only occur between defenders and defenders or midfielders and midfielders. How many:
(1) different possible lineups of the 11 players on the field at the end of the match are there?
(2) different possible match processes are there (if the 11 players on the field at any time are different, the matches are considered different processes)?
15. (1) Let the total number of substitutions in the match be $t$, where $t=0,1,2,3$.

When $t=0$, 11 players play the entire match, which is only 1 way.
When $t=1$, the substituted player can be a midfielder or a defender, resulting in $\mathrm{C}_{2}^{1} \mathrm{C}_{4}^{1} + \mathrm{C}_{2}^{1} \mathrm{C}_{4}^{1} = 16$ ways.

When $t=2$, the substitutions can be two midfielders, two defenders, or one midfielder and one defender, resulting in $\mathrm{C}_{4}^{2} + \mathrm{C}_{4}^{2} + \left(\mathrm{C}_{2}^{1} \mathrm{C}_{4}^{1}\right)\left(\mathrm{C}_{2}^{1} \mathrm{C}_{4}^{1}\right) = 76$ ways.

When $t=3$, the substitutions can be two midfielders and one defender, or two defenders and one midfielder, resulting in $\mathrm{C}_{4}^{2} \mathrm{C}_{2}^{1} \mathrm{C}_{4}^{1} + \mathrm{C}_{4}^{2} \mathrm{C}_{2}^{1} \mathrm{C}_{4}^{1} = 96$ ways.
In total, there are $1 + 16 + 76 + 96 = 189$ ways.
(2) When $t \geqslant 2$, each final lineup corresponds to $t!$ different match processes. Therefore, the total number of different possible match processes is $1 + 16 + 76 \times 2! + 96 \times 3! = 745$ ways.