The way to do this is truncate after the one you used simple_formatin the line. Since truncate preempts the default string, you should use the option escape: false.
> myString = "Apple’s New Laptop"
> truncate(simple_format(myString), escape: false)
> => "<p>Apple’s New Laptop..."
> truncate(simple_format(myString), escape: false, length: 19)
> => "<p>Apple’s..."
This can create unbalanced HTML tags, for example, by clipping </p>, so use with caution.