As was stated above answer by GovEcon is wrong.
Wiki defines p in the above formula as: "where p is the total number of explanatory variables in the model (not including the constant term), and n is the sample size."
The parameters three parameters. Excluding the intercept (constant/beta0) p = 2.
That being said it would be easier to calculate R^2 as follows.
Formula for R^2 adjusted can be given as
R^2 adjusted = 1 - (n-1)(MSE/SST), MSE = SSE/(n-p-1)
= 1- (n-1)[(SSE/n-p-1)/SST] = 1- [(n-1)/(n-p-1)]*(SSE/SST)
If you recall definition of that R^2 adjusted controls for increase in R^2 due to increase in parameters then it makes sense that removing [(n-1)/(n-p-1)] should give you R^2
R^2 = 1- SSE/SST
Check by plugging in
SSE/SST = 1-R^2
R^2 adjusted = 1- [(n-1)/(n-p-1)]*(1-R^2) = original formula
Then, R^2 adjusted = 1 - (n-1)*(MSE/SST) = 1- (15-1)(8224/1436706) = ~.9198
R^2 = 1- SSE/SST = 1- 98690/1436706 = ~.931 NOT .9371
Note: the anova table is already rounded MSE = SSE/ (n-p-1) = 98690/(15-2-1) = 8224.16666 = ~8224. So discrepancies with table arise from here.
Aside: I don't know how to format equations and don't have time to do it now, but I do not want the current answer to mislead more people.