CL can handle a large SLOC, as evidenced by the fact that the huge compiler such as SBCL itself is written in CL. But it won't be as popular as Java or C++ are, so it would become a problem when CL faces a project which is "large as in company".
CLer: Your language isn't suited for the enterprise. You need a hundred developers to do what we do with five.
There are some CL code bases with millions of lines. But even a million line in todays terms is not much for some companies which are using other languages. If we look back, the operating system and basic environment (GUI, IDE, basic apps) of the Lisp Machine OS was around 500 kloc. Later versions with more stuff and some applications were nearing 2 Mloc. The commercial CL companies (Franz, Harlequin/LispWorks, Lucid, Xerox, TI, LMI, Apple, Goldhill, DEC, ...) usually should have developed code bases with +1MLOC already in the 80s / early 90s. Some Common Lisp based CAD software was/is in the range of 5-10 MLoc. Some application code might be much larger. For example Boeing has whole jet aircrafts designed in Lisp using the now discontinued iCAD application.
> so it would become a problem when CL faces a project which is "large as in company".
Common Lisp has been used in environments with up to 300 developers. This is not really a large number, but a larger number of what people typically think of a Lisp project. Symbolics, the Lisp Machine company, had at max 1000 employees - with probably a third of that software developers. Lucent developed network switches in the 80s/90s with 100+ Lisp developers. ITA was developing their flight search engine with a 100+ team with a lot Lisp developers. There are also smaller companies with a long history - for example Cyc is being developed using Lisp since thirty years.
One problem was/is finding these people. An old saying was that there were more Lisp Machines than developers able to use them. Today it would be even more of a problem, since the number of interesting Lisp projects at universities is smaller than what we had in the 80s/90s. Thus fewer students get in contact.
Probably a good idea to visit the European Lisp Symposium in Brussels, April 2017. Meet some fellow Lisp users from academia, industry, ...