The weight of minimum spanning tree in graph $G$, calculated using Kruskal's algorithm is:

Using Kruskal’s algorithm, arrange all edges in increasing order of weight:

$2,\ 3,\ 4,\ 5,\ 6,\ 7,\ 8$

Now select the minimum weight edges without forming a cycle.

Selected edges are:

$2,\ 3,\ 4,\ 6$

Here, edge $5$ is skipped because it forms a cycle.

So, total weight of minimum spanning tree is:

$2+3+4+6=15$