Turbomax 15W-40 CI4/SL is marketed by Morrison Lubricants. They list it in 5 L & 18 L pack sizes.
It is described as a “high-performance heavy duty diesel engine oil” formulated with “Nano Technology” to suit modern low emission diesel engines (including those with EGR systems).
There is also a similarly named product Castrol CRB Turbomax 15W-40 CI-4/SL/E7 (or “Turbomax” variant from Castrol). The product from Castrol claims advanced “DuraShield™ Boosters” to help protect against soot aggregation, wear, deposits etc.
Typical specifications (for Castrol’s Turbomax) include meeting API CI-4 / SL specification, and also meeting heavy duty diesel oil standards (e.g. ACEA, OEMs) as per the datasheet.