You can either patch the binary

sudo patchelf --replace-needed libalpm.so.14 libalpm.so.15 "$(which paru)"

Or install paru-git

sudo pacman -S --needed base-devel
git clone https://aur.archlinux.org/paru-git.git
cd paru-git
makepkg -si

Or do both, patch the binary, then use it to install paru-git (which is what i did)