I have searched for many definitions of divisibility and they all seem to go like this:
Let $a, b \in \mathbb{Z}$ then $b$ is divisible by $a$ if there exists $c \in \mathbb{Z} : b = ac$.
Is divisibility defined only between integers? Is it incorrect to say that 3 is divisible by 1.5?
You may generalize the concept of divisibility to general rings. So you have to be specific. Usually we talk about divisibility in terms of $\Bbb{Z}$ because if we introduce $\Bbb{Q}$ or $\Bbb{R}$ things get boring, everything divides everything (except weirdness around $0$)!
So if you say " $3$ is divisible by $1.5$", you have to specify. Are you in $\Bbb{Z}$? Then $1.5$ doesn't exist! Are you in $\Bbb{Q}$? Then yes, because everything divides everything then! (again except issues with $0$)
For example if you consider the ring of polynomials with coefficients in $\Bbb{R}$, $x+2$ divides $x^2-4$. There are other examples of divisibility in strange rings.