Well, assuming all of your modelling assumptions are fulfilled, the modelling techniques do not differ and also assuming $R^2$ is the only model characteristic that differs between the models, I would consider a Student’s t-test (assumptions permitting) or Wilcoxon-Mann-Whitney test on the $R^2$s. In any case I would try to get a larger sample (costs permitting).
You can read more about different model selection measures, particularly AIC, here.
If different modelling techniques were used you may find this interesting.
