An ice cream truck that plays loud music is circling Bulan’s neighborhood. ${C}({t})$ models the volume of the music (in ${dB}$ ) that Bulan hears, ${t}$ minutes after the truck arrives in her neighborhood. Here, $t$ is entered in radians.

$C(t)=-15 \cos (\frac{2 \pi}{15} t)+65$

How many minutes after the truck arrives does the volume first reach $75 {~dB}$ ?

Round your final answer to the nearest tenth of a minute.