(1 + year | ID0) specify a random intercept and a random slope, both grouped by ID0. See the cheat sheet for an explanation of the syntax.

15 unique IDs times (intercept + slope) gives 30 random effects. You don't have sufficient observations to support the model.

(1 + year | ID0) specify a random intercept and a random slope, both grouped by ID0, and additionally their correlation. See the cheat sheet for an explanation of the syntax.

15 unique IDs times (intercept + slope + correlation) gives 45 random effects. You don't have sufficient observations to support the model.

(1 + year | ID0) specify a random intercept and a random slope, both grouped by ID0. See the cheat sheet for an explanation of the syntax.

15 unique IDs times (intercept + slope) gives 30 random effects. You don't have sufficient observations to support the model.

(1 + year | ID0) specify a random intercept and a random slope, both grouped by ID0. See the cheat sheet for an explanation of the syntax.

15 unique IDs times (intercept + slope) gives 30 random effects. You don't have sufficient observations to support the model.