Notice that there are $3$ terms with $2$ so probably it will be of form $(a+b+c)^2$ $$(a+b+c)^2=a^2+b^2+c^2+2(ab+ac+bc)\\\a^2+b^2+c^2=10\\\ab=\sqrt{15}\\\ac=\sqrt{10}\\\bc=\sqrt{6}\\\b^2+c^2=10-a^2\\\a^2b^2+a^2c^2=25\\\a^2(b^2+c^2)=25\\\a^2(10-a^2)=25\\\10a^2-a^4-25=0\\\a^4-10a^2+25=0\\\\(a^2-5)^2=0\\\a=\sqrt{5}\\\ab=\sqrt{15}\implies b=\sqrt{3}\\\bc=\sqrt{6}\implies c=\sqrt{2}$$ So the answer is $\sqrt{2}+\sqrt{3}+\sqrt{5}$