The domain of the quadratic function $\displaystyle{f{{\left({x}\right)}}}={3}{{x}}^{{2}}+{12}{x}+{15}\usepackage{cmbright}\Huge\$ is all real numbers. Find the range of the function.

The range is all real numbers $\displaystyle{f{{\left({x}\right)}}}\usepackage{cmbright}\Huge\$ such that $\displaystyle{f{{\left({x}\right)}}}\ge\usepackage{cmbright}\Huge\$ _____.