It's always best to use the oil recommended by the manufacturer as they have designed and tested the motorcycle with specific oil formulations in mind. The manufacturer's recommended oil will be formulated to meet the necessary viscosity and performance requirements for the engine.
Typically, for a Suzuki Gixxer 155 or any motorcycle, it is advisable to use a high-quality, motorcycle-specific engine oil that meets the required specifications. Look for oils that have the proper viscosity rating, such as 10W-40 or 10W-30, as specified by Suzuki.
Additionally, ensure that the engine oil you choose meets the necessary standards, such as API (American Petroleum Institute) rating, which is commonly indicated by the letters "SJ" or higher. Some motorcycle-specific oils may also carry JASO (Japanese Automotive Standards Organization) certifications, such as JASO MA or JASO MA2, which are designed specifically for motorcycles.
It is important to note that oil preferences can vary among riders based on climate conditions, riding style, and personal preferences. If you have any doubts or would like specific recommendations for your Suzuki Gixxer 155, I would recommend consulting the owner's manual or contacting a Suzuki dealership or authorized service center for the most accurate and up-to-date information.